1. Field of the Invention
The invention refers to a roll refiner or roller mill comprising at least four rolls for processing viscous materials by homogenizing and grinding procedures, in particular chocolate masses, printing paints, and the like. The invention equally refers to a method for operating the roll refiner.
2. Description of the Prior Art
Roll refiners having one or several rolls adjustable as to their rotational speeds are known in the art. One such roller mill disclosed in French. Pat. No. 111 58 23 comprises three rolls and has the rotational speed of its discharge roll arranged to be adjustable with respect to the rotational speed of the middle roll. A particular embodiment of this roller mill is provided with feed rolls rotating at a fixed speed ratio to each other. The discharge roll, on the other hand, is adjustable in an infinitely variable manner, thereby to influence the degree of spread of the processed material, dependent upon the difference in rpm between the middle roll and the last roll. The degree of processing of the material is influenced by way of the last roll gap, while at the same time the rotational speeds of the second and third rolls are regulated.
Another roll refiner disclosed in the German Auslegeschrift No. 10 33 995 is arranged to have the rotational speed of any of its rolls, in particular the rotational speed of the two feed rolls, adjustable in an infinitely variable manner.
Regulating the rotational speeds of both feed rolls is more effective for regulating the quantity of a material fed the roll refiner per unit time than regulating the rotational speed of only one of the feed rolls. In particular, if the two feed rolls are arranged to rotate in a fixed rotational speed ratio to each other, this will make the range of rotational speeds covered by regulation, and thus the pulled-in quantity of material greater, than if the speed of only one of the feed rolls is regulated.
A roll refiner disclosed in the British Pat. No. 10 80 782 is arranged to have the rotational speeds of both or its feed rolls regulated in an infinitely variable manner; however, this roll refiner was built for batch production with return flow.
Finally, the German Pat. No. 10 30 553 discloses a calender mill, in which each roll may be regulated in regards to its rotational speed independent of the others, or else together with the others and in the same sense. However, a regulating system of this kind is comparatively complicated.